Experimental Study Of Direct-injected Methanol Ignited By Diesel

At present,the increasingly serious energy problem,environmental pollution and global climate problem promote the development of internal combustion engine to clean and renewable energy applications.Among them,the development of methanol diesel dual fuel engine has a broad prospect in China.In order to explore the combustion process in the cylinder of this kind of engine,this paper carried out the visualization experiment of direct injected methanol flame ignited by diesel,and obtained the shadowgraph and natural luminescence images of the flame.Based on the images of direct injected methanol flame ignited by diesel obtained by experiments,this paper studies the development characteristics and local flame structure characteristics of this kind of flame.In this paper,a set of flame image processing algorithm is developed to extract the combustion characteristics of the flame.Finally,the overall development characteristics,ignition delay period,lift-off length and spatial integrated natural luminance of the direct injected methanol flame ignited by diesel under different diesel injection pressures,methanol injection pressures,combustion temperatures and different injector arrangements are compared and analyzed,as well as the differences between the direct injected methanol flame ignited by diesel and the directly injected diesel flame.In the direct injected methanol flame ignited by diesel,the ignition area mainly appears in the position where diesel is relatively rich.Then,the flame propagation speed in the diesel fuel path is higher than that in the methanol concentration zone.When the methanol region is ignited,the flame begins to deviate from the axis of the diesel injector.It can be found from the image of the local area of direct injected methanol flame ignited by diesel that at the end of combustion,there are still parts of the methanol concentration area that has not been completely burned.Moreover,the area of the unburned area in the diesel blind area is significantly larger than that in the downstream of the diesel injection beam,which explains the phenomenon of unburned hydrocarbon emission in the related whole machine experiments.The variation of diesel injection pressure mainly affects the mixing process with methanol spray.Under the condition of high-pressure diesel injection,the mixing of diesel and methanol is better,and the time of methanol ignition is advanced.However,the methanol also inhibits the ignition of diesel.After the methanol is ignited,the soot oxidation process is accelerated,so the spatial integrated natural luminance of the direct injected methanol flame ignited by diesel is decreased faster than that of the direct injection diesel flame.Because diesel combustion is the main process of producing soot,the flame brightness decreases under the condition of high-pressure diesel injection.The influence of methanol injection pressure on the flame combustion characteristics is mainly reflected in two aspects.One is the influence on the mixture quality of methanol and air and the spatial distribution of concentration,which is reflected in the flame propagation speed and flame distribution after the methanol area is ignited under the condition of high-pressure methanol injection.In addition,the change of methanol injection pressure also changes the air motion in the ignition area,which is reflected in the different degree of flame deviation from the axis of the injector at the initial stage of the flame under different methanol injection pressure,and this change also has a certain impact on the ignition delay period.The increase of ambient gas temperature promotes the combustion process of direct injected methanol flame ignited by diesel.With the increase of temperature,methanol and diesel have better atomization characteristics and higher reactivity.The flame's ignition delay is shortened.After ignition,the flame propagation speed in methanol area is accelerated and the overall combustion duration is shortened.When the injector layout adjustment makes the intersection area of methanol and diesel spray move down,the ignition delay period of direct injected methanol flame ignited by diesel is more stable and regular.The inhibitory effect of methanol on ignited diesel oil was milder before ignition.However,some diesel flames failed to enter the spray area of methanol completely before blending with methanol.Moreover,after the ignition of diesel,the reaction gas rapidly heats up and expands,and the density correspondingly decreases,so the air flow induced by methanol injection plays a more important role.